Various types of apparatus have been used to lay subterranean conduit. Over the years a number of trenching devices have been developed to meet the needs of underground contractors. When doing subterranean work, various types of ground conditions and obstacles are encountered. The ground to be worked may be stable or unstable, it may contain numerous rocks or other obstacles such as utility lines and other underground conduits, or it may have a high water table. Each different type of ground condition requires that the underground contractor pay particular attention to the safety of the workmen and that procedures designed to achieve the greatest efficiency are followed.
Where the ground is stable and maintains its form when a deep trench is excavated therein, excavation and conduit laying can be done quickly and efficiently without significant danger of the trench walls collapsing. Frequently, in stable ground conditions a conduit laying apparatus such as a trencher with a trench boot is used to cut the trench and lay a uniform layer of fill material in the bottom of the trench upon which the conduit is positioned and aligned. Also, since the trench boots have walls to shore up the walls of the trench, the use of a trench boot provides an added safety precaution which protects the workmen within the trench from collapse of the trench walls.
In unstable ground conditions, the use of conduit laying apparatus such as trench boots or trench boxes becomes more critical. Unstable ground is more prone to collapse into the trench. This creates significant problems to underground contractors. Life and limb of the workmen within the trench can be endangered by collapsing trench walls. Further, it is not infrequent that progress in laying conduit is slow and tedious, because delays are caused by collapsing walls and other problems caused by the unstable ground.
When a trench boot or trench box is not used in unstable ground conditions, the walls of the trench must be sloped back at an angle of repose such that the walls are not likely to collapse into the trench. This means that the excavator must remove considerably more earth from the trench, causing time delays and added expense. For example, if the instability of the ground required that the trench walls be sloped back 45 degrees, for a trench two (2) feet wide and ten (10) feet deep, the excavator must remove 120 cubic feet of earth for each foot of length of the trench. This is an additional 100 cubic feet in excess of the 20 cubic fee for the needed trench. In this instance, excavator time is increased five-fold, and since the use of heavy equipment is quite expensive, the cost of the trenching project is also increased proportionally.
In rocky ground or earth containing obstacles such as utility lines, the underground contractor encounters different and challenging problems. Certain kinds of excavating implements cannot be efficiently used or used without damage either to the implement or the utility line. This severely limits the efficiency of the underground contractor in laying conduit within a trench. In some instances, the use of certain types of excavators and trench boxes becomes cost prohibitive due to the time delays involved in working around obstacles within the trench.
Unique types of problems are presented where the conduit to be laid is in an area where there is a high water table making the ground unstable and difficult to trench. Often, as rapidly as the trench is excavated, it begins to fill with ground water which makes it extremely difficult to lay a fill material bedding or the conduit in the bottom of the trench. In some instances, continuous pumping of the ground water from the trench is futile.
As can be easily seen, the laying of subterranean conduit presents many and varied problems for the underground contractor. Consequently, over the years, there have been a number of implements and apparatus which have been developed to assist the underground contractor in laying conduit within a trench. There have been trench boxes and trench boots utilized with many different types of excavating implements and in a variety of contexts.
For example, there were ditching and tile laying machines which were developed as early as the 1880's in which a plow opened a ditch into which the tile was to be laid. A hopper or chute was attached behind the plow through which tiles were fed and delivered to the bottom of the ditch and a fill material was carried down the chute to cover the positioned tile. However, the plow/hopper apparatus had significant limitations. The ditch created was not very deep because as the plow was placed deeper beneath the ground surface it became more difficult to pull the plow through the earth. Further, many a plow has been broken upon striking a rock hidden below the surface. More importantly, it was extremely difficult to lay tile in a straight line because plows have a tendency to move and deflect along a path of least resistance. Because of the limitations of laying tile using plows to dig the ditch, other types of trenching apparatus were developed.
Later, as trenchers with trenching booms were developed it became easier to dig trenches in alignment by moving a minimum amount of earth. The trenching boom of a trencher is lowered into a trench to the desired depth and digging bucket mechanism adapted for digging an elongated earthen trench is used to cut the trench in which the conduit is to be laid. The efficiency of the underground contractor was improved tremendously by the advent of trenchers, particularly where the trench was to be excavated under stable ground conditions. The trencher could remove only the earth necessary to open the appropriate size of trench.
However, under unstable ground conditions, the walls of the trench frequently would slough into the trench behind the trencher boom before conduit could be laid. To minimize this problem trench boots were developed. The trench boots were typically boxlike apparatus attached behind the trencher boom. The development of trenchers with trench boot mobile housings which followed behind the digging bucket mechanism of the trencher boom within the trench became an integral part of efficiently laying conduit within a trench. Illustrative examples of the type of trench boots developed to be used in conjunction with trenchers are U.S. Pat. No. 3,605,419, issued to M. E. Wells, Sept. 20, 1971, entitled "Method and Apparatus for Laying Pipe," and U.S. Pat. No. 4,028,902, issued to Courson et al., June 14, 1977, entitled "Apparatus for Laying Elongated Flexible Tubing." However, most trench boots used with trenchers are designed to lay only flexible pipe.
Despite the usual efficiency of trench boots used with trenchers, there are certain types of ground conditions and obstacles encountered which make the use of a trencher unfeasible. For example, it is not advisable to use a trencher to excavate a trench in areas where there are numerous utility lines. Each time a utility line is encountered, the trenching boom with the trench boot attached thereto must be removed from the trench and the earth surrounding the utility line must be cleared away, either manually or using some other type of excavating implement such as a backhoe. Thus, additional heavy equipment must be continuously on call to relieve the trencher when a utility obstacle is encountered. This significantly increases the cost of the project and decreases the efficiency of the underground contractor.
More importantly, it is not unusual in such instances that the operator of the trencher will sever utility lines within the trench. This interjects tremendous delays and can be extremely dangerous. The utility lines must be repaired before the conduit-laying project can continue. The utility company must be notified and the subterranean work ceases until a utility company crew can repair the problem. Further, if the utility line severed is a gas line, there is a serious chance of an explosion and the work area as well as the surrounding area may have to be evacuated until the problem is remedied.
Independent of those types of problems, since the trench boot must be removed from the trench, the pipe must be laid manually at the bottom of the trench without the safety of the trench boot walls. Consequently, in the vicinity of the utility line it is not uncommon that the walls of the trench must be sloped back at an angle of repose sufficient to assure that the walls of the trench will not collapse on the workers as they are manually laying the conduit. This can involve moving tremendous amounts of earth causing additional delays. Once the conduit is laid beneath the utility obstacle the trencher with the trench boot attached can be lowered into the trench and excavation can recommence. However, if another obstacle is encountered, the same tedious and time consuming process must be undertaken. For these and other significant reasons, use of a trencher with a trench boot attached thereto frequently is not the most cost effective way to lay conduit.
Trench boxes have been designed to assist in laying conduit in areas where it is not advisable to use a trencher. Trench boxes usually comprise spaced walls supported by transverse rods which hold the walls in a spaced relationship. When a deep trench is required, the trench boxes are merely stacked one on top of the other until the desired height is reached. The walls of the trench box provide the abutment against which the walls of the trench would fall in the event of a collapse. In this manner workers within the trench box are protected from trench wall collapse.
Under stable ground conditions, it is not unusual that the excavating machine (e.g., a backhoe) can excavate a trench in advance of the trench box. The trench carved out of the earth is necessarily wider than the trench box and once the conduit is laid on the bottom of the trench within the trench box, the trench box may be advanced for continuing the conduit-laying procedure.
Under unstable ground conditions, the use of a trench box becomes much more complex. Excavation of the trench in advance of the trench box is not feasible because the walls of the trench tend to collapse before the trench box can be advanced. As a result, conditions may require that a different method be used. One common method that has been used involves placing the trench box on the surface of the ground where the trench is to be excavated. Earth is excavated from within the trench box and the trench box is tapped down into place gradually as the earth within the trench box is removed. This procedure is continued until the trench box is located at the desired depth. The conduit can then be laid within the trench box on the bottom of the trench. To advance the trench box, the underground contractor cannot remove the trench box from the trench because the unstable walls of the trench may collapse about the freshly laid conduit before the connecting conduit can be laid. Therefore, to lay additional conduit the trench box is pulled forward and its forward end tilted at an angle because it rests on unexcavated earth. Then, more earth is excavated from within the trench box. The forward end of the trench box is tapped down until it reaches the desired depth and levels off with the rear of the trench box. Additional conduit can be laid once the trench box reaches the desired depth. This procedure is performed repeatedly until the desired distance of conduit is achieved.
If a utility line is encountered the trench box usually must be removed from the trench and the area around the utility must be cleared so that conduit can be laid manually in the vicinity of the utility obstacle.
Further, with most trench box apparatus there is no facility for automatically laying a fill material bedding on-grade upon which the conduit can be laid. Usually, the fill material must be leveled manually before the conduit can be positioned. Consequently, although in some instances it may be more cost effective to use a trench box to lay conduit under certain ground conditions, it is still an extremely time consuming, difficult and expensive procedure.
Additional problems are created when ground water rapidly fills the trench. With most trench boxes, there is no facility to handle such seepage and pumps are frequently used to extract as much of the ground water as possible. Where the water table is extremely high, the use of a trench box may not be as effective because the ground water moves the soil in too rapidly to allow the laying of the conduit.
One device which has been developed to extract ground water from a trench is illustrated in U.S. Pat. No. 4,462,715, issued to Ashbaugh, July 31, 1984, entitled "System for the One-Step Dewatering of a Trench and the Construction of a Pipeline Bed." The device used is a stone-filled box which is pushed along the trench in increments as the trench is excavated ahead of the box. Simultaneously, the box dispenses stone out the rear end of the box to form a bed which shores up the side of the trench and upon which conduit can be laid. A pump is provided inside the stone-filled box to extract water which has seeped into the box. With this device, however, the conduit is laid on the bed of stone discharged from the stone-filled box. Consequently, if the trench is quite deep or if the water table is quite high the sides of the trench may collapse or water may seep into the trench and the bedding layer before conduit can be laid.
Despite the development of various types of devices, trench boots used in conjunction with trenchers, trench boxes, trench hoppers or chutes following plows and other types of devices, there are some problems that heretofore have remained unsolved. For example, it is extremely difficult to maintain grade and alignment of conduit being laid in a deep trench. In the past, grade and alignment have been matters of estimation and approximation by the underground contractor or the worker operating the trenching devices. As more sophisticated technology became available, it became possible to use lasers in the bottom of a trench to assist in alignment and maintaining grade. However, intrench laser systems cannot always be used to accurately align a conduit or maintain it on-grade, particularly where severe conditions exist because water and/or sand move into the conduit and deflect or obstruct the laser beam.
Also, the normal procedure for conduit laying, as outlined in the "Caterpillar Equipment Performance Guide Book" is for an excavator to dig a portion of the trench and then to sit idle while the conduit is set. Once the conduit is set, the excavator commences digging on the next portion of the trench. With this procedure, the excavator is actually digging only about half the time.
The handling of the conduit itself has also presented problems. Where the conduit is heavy cement sewage pipe, it is difficult for one worker to lower the pipe into the trench, or to position the pipe, particularly when the trench is rather deep. When the pipe is flexible pipe it is critical that the pipe be delivered to the bottom of the trench in a manner which will not kink or damage the pipe. Since different types of pipe or conduit present different types of problems, heretofore there has not been a trench boot or trench box which readily enables the underground contractor to simultaneously lay two types of conduit, namely flexible and rigid conduits.
Thus, although there have been a number of developments in trench boots and boxes which assist in the laying of conduit within a trench, it would be an improvement to provide an apparatus in which laying subterranean conduit under a variety of ground condition would be efficient and economically justifiable. It would be an improvement to provide a structure which could be separated quickly and easily to avoid obstacles such as utility lines within a trench while still permitting conduit to be laid with the assistance of that structure in the vicinity of and beneath the utility line. It would be a further improvement to provide an operations-efficient apparatus which can be operated to significantly reduce the amount of earth that must be excavated from and back filled into a trench, and which requires a minimum of large excavating equipment, and permits such excavating equipment to be engaged in the trench-digging function almost continuously. It would be another improvement to provide an apparatus which would have dewatering capability to assist in the laying of conduit in areas with high water tables. It would be still another improvement to provide a conduit lowering system which would automatically deliver and align conduit within the trench. It would be a further improvement to provide a grade and alignment system, heretofore not provided with trench boxes, which would increase the operator's ability to maintain the apparatus on-grade and in alignment. It would be another improvement to provide an apparatus which would permit more than one type of conduit to be laid in alignment and ongrade simultaneously. It would be still another improvement to provide an apparatus which dispenses the exact amount of fill material desired into the trench at the proper time and place, thereby eliminating waste of labor, material and equipment time.